1. Field of the Invention
The invention relates generally to arc lamps and more particularly to arc lamps for use with fiber optic bundles.
2. Description of the Prior Art
Arc lamps are used to provide intense point sources of light for applications such as instrumentation and projection. Medical endoscopes are one type of application. In endoscopes, the arc lamps serve as illuminators of fiber optic bundles that allow visual examination of the body canals and adjacent organs without conventional surgery. Arc lamps are also used in industrial endoscopes to examine structures and components which are difficult to inspect visually, such as the interiors of jet engines.
Recently, medical science has started to use fiber optic bundles to examine smaller body canals, such as the coronary arteries. In order to achieve this, the fiber bundles cannot exceed one millimeter in diameter. In the past, fiber bundles have been at least four millimeters in diameter. In order to achieve fiber bundles of less than one millimeter in diameter, each individual fiber cannot exceed two hundred microns in diameter. It is thus necessary to have a light source which can provide a highly intense point of light to a fiber of two hundred microns or less.
A typical prior art arc lamp system for use with a fiber optic bundle is shown in FIG. 1 and is designated by the general reference number 10. An arc lamp 20 is generally symmetrical about an axis 22 and includes a base 24, a body 26, an anode 28, a cathode 30, a plurality of cathode support arms 32 and a window assembly 34. The base 24 is generally formed out of iron. The body 26 is usually made of a ceramic material.
The body 26 includes a concave cavity 40 which defines a curved reflective surface 42. Reflective surface 42 has a reflective metal coating deposited thereon. Anode 28 passes from the base 24 through the body 26 and extends from the back of reflective surface 42 into cavity 40 along axis 22. Cathode support arms 32 extend radially from body 26 toward axis 22. Cathode 30 is mounted to support arms 32 along axis 22. The window 34 fits sealingly against body 26 so that cavity 40 is gas tight. Window 34 is made of a transparent material. In operation, the cavity 40 is filled with an inert gas, such as xenon, at a pressure of several atmospheres. The lamp is illuminated when a breakdown voltage is present across the arc gap, thereby resulting in an illuminating flow of electrons (i.e., arc discharge) across the gap from the cathode 30 to the anode 28. Typically, such lamps operate from about one hundred fifty to eight hundred watts.
A first heat sink 50 is attached to base 24. Heat sink 50 absorbs the heat from base 24. A second heat sink 52 is attached to window 34 to draw off heat generated in the window 34.
The light 60 emerges from arc lamp 20 and passes through a lens 64. Lens 64 is needed to concentrate light 60 into a beam small enough for use with a fiber optic bundle 68. Before light 6 enters bundles 68, it is filtered by a cold mirror 70. Cold mirror 70 reflects visible light 74 to bundle 68, but allows infrared light to pass through to a third heat sink 80. Heat sink 80 dissipates the heat from infrared light 76.
There are several problems with this prior art system. One problem is that the system is bulky and involves a large number of components. Another problem is that the positioning of such components as the reflector 42, with respect to the cathode 30, lens 64, and mirror 70 must be exact. Even slight deviations in the alignment of these components can be critical. Another problem is that the reflector forms holes in the beam of light. These beam hole patterns in the light prevent the generation of a uniform light source.
Another prior art system is shown in U.S. Pat. No. 3,770,338, by James Helmuth. A light conducting pipe is inserted into an arc lamp envelope perpendicular to the electrodes. The light conducting pipe gathers light from the entire arc plume. However, the plume is not uniform in intensity and therefore, the light collected is asymmetrical. In addition, the light provided is not a highly focused intense point of light needed for optical fibers of two hundred microns or smaller.